This blog features my weekly column called "What's up in the sky". It is published every Saturday in the Ellensburg newspaper, Daily Record (http://www.kvnews.com/). While my postings will be most accurate for Central Washington, readers throughout the northern USA may find something of use.

Wednesday, March 15, 2017

The Ellensburg WA sky for the week of 3/18/17

Saturday: The
elusive Mercury is a half a fist held upright and at arms length above due west
at 7:40 p.m. The much brighter Venus is about one fist to the upper right of
Mercury.

Sunday: Mars
is two fists above due southwest at 8:30 p.m.

Monday: Look
up in the sky. It’s a plane. It’s a bird. No, it’s the vernal equinox. The
vernal equinox!? Spring starts at 3:30 a.m. Pacific Daylight Time. The first
day of spring is often called the vernal equinox. This label for the day is misleading.
The vernal equinox is actually the point in the sky where the Sun’s apparent
path with respect to the background stars (called the ecliptic) crosses the
line that divides the stars into north and south (called the celestial
equator). This point is in the constellation Pisces the fishes. At the vernal
equinox, the Sun is moving from the southern region of background stars to the
northern region. Since the Sun crosses the vernal equinox at night, tomorrow
will actually be the first full day of spring.

Because the
Earth slowly wobbles like a spinning top, the vernal equinox is slowly moving
into the constellation Aquarius. By the year 2597, the vernal equinox will
reach the constellation Aquarius and the “Age of Aquarius” will begin. Until
then, we’ll be in “the age of Pisces”.

Tuesday: The
Milky Way is pretty easy to spot on the early spring sky. Just look up.
Everything you see in the sky, including that bird that just startled you, is
in the Milky Way. But, even the path of densely packed stars in the plane of
our galaxy that look like a river of milk is easy to find. Look due south at 9
p.m. Follow the fuzzy path just to the left of the bright star Sirius two fists
above the horizon, to the right of the bright star Procyon four and a half
fists above the south horizon, through Capella six fists above the west
horizon, through W-shaped Cassiopeia three fists above the northwest horizon,
and down to due north where the bright star Deneb sits just above the horizon.

Wednesday: Astronomers are often fascinated with large objects. Planets that
could fit 1000 Earths (Jupiter). Stars that would fill up the entire inner
Solar System (Betelgeuse). Galaxies with 400 billion stars (Milky Way). But
what about the smallest objects? One of the smallest stars is Proxima Centauri,
the closest known star other than our Sun. It is about 12% of the mass of the
Sun. Last year, astronomers even announced the discovery of an Earth-sized
planet orbiting Proxima Centauri indicating that even very small starts can
have planets. The smallest theoretically possible star would be about 7.5% of
the mass of the Sun. Any smaller and it could not support fusion reactions. For
more on small stars, go to http://goo.gl/EHBdOX.

Thursday: Jupiter is one fist above the east-southeast horizon at 10 p.m.

Friday: If you want to put
somebody off, tell her or him to wait until Deneb sets. At Ellensburg’s
latitude of 47 degrees, Deneb is a circumpolar star meaning it never goes below
the horizon. At 9:32 p.m., it will be as close as it gets to the horizon, about
two degrees above due north. Watch it reach this due north position about 4
minutes earlier each night.

The
positional information in this column about stars and planets is typically
accurate for the entire week. For up to date information about the night sky,
go to https://nightsky.jpl.nasa.gov/planner.cfm.